package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

/**
 * Abstract base class for performing read operations of Lucene's low-level
 * data types.
 */
public abstract class DataInput implements Cloneable {

    private boolean preUTF8Strings; // true if we are reading old (modified UTF8) string format

    /** Call this if readString should read characters stored
     *  in the old modified UTF8 format (length in java chars
     *  and java's modified UTF8 encoding).  This is used for
     *  indices written pre-2.4 See LUCENE-510 for details. */
    public void setModifiedUTF8StringsMode() {
        preUTF8Strings = true;
    }

    /** Reads and returns a single byte.
     * @see DataOutput#writeByte(byte)
     */
    public abstract byte readByte() throws IOException;

    /** Reads a specified number of bytes into an array at the specified offset.
     * @param b the array to read bytes into
     * @param offset the offset in the array to start storing bytes
     * @param len the number of bytes to read
     * @see DataOutput#writeBytes(byte[],int)
     */
    public abstract void readBytes(byte[] b, int offset, int len) throws IOException;

    /** Reads a specified number of bytes into an array at the
     * specified offset with control over whether the read
     * should be buffered (callers who have their own buffer
     * should pass in "false" for useBuffer).  Currently only
     * {@link BufferedIndexInput} respects this parameter.
     * @param b the array to read bytes into
     * @param offset the offset in the array to start storing bytes
     * @param len the number of bytes to read
     * @param useBuffer set to false if the caller will handle
     * buffering.
     * @see DataOutput#writeBytes(byte[],int)
     */
    public void readBytes(byte[] b, int offset, int len, boolean useBuffer) throws IOException {
        // Default to ignoring useBuffer entirely
        readBytes(b, offset, len);
    }

    /** Reads two bytes and returns a short.
     * @see DataOutput#writeByte(byte)
     */
    public short readShort() throws IOException {
        return (short) (((readByte() & 0xFF) << 8) | (readByte() & 0xFF));
    }

    /** Reads four bytes and returns an int.
     * @see DataOutput#writeInt(int)
     */
    public int readInt() throws IOException {
        return ((readByte() & 0xFF) << 24) | ((readByte() & 0xFF) << 16) | ((readByte() & 0xFF) << 8) | (readByte() & 0xFF);
    }

    /** Reads an int stored in variable-length format.  Reads between one and
     * five bytes.  Smaller values take fewer bytes.  Negative numbers are not
     * supported.
     * @see DataOutput#writeVInt(int)
     */
    public int readVInt() throws IOException {
        /* This is the original code of this method,
         * but a Hotspot bug (see LUCENE-2975) corrupts the for-loop if
         * readByte() is inlined. So the loop was unwinded!
        byte b = readByte();
        int i = b & 0x7F;
        for (int shift = 7; (b & 0x80) != 0; shift += 7) {
          b = readByte();
          i |= (b & 0x7F) << shift;
        }
        return i;
        */
        byte b = readByte();
        int i = b & 0x7F;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7F) << 7;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7F) << 14;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7F) << 21;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        assert (b & 0x80) == 0;
        return i | ((b & 0x7F) << 28);
    }

    /** Reads eight bytes and returns a long.
     * @see DataOutput#writeLong(long)
     */
    public long readLong() throws IOException {
        return (((long) readInt()) << 32) | (readInt() & 0xFFFFFFFFL);
    }

    /** Reads a long stored in variable-length format.  Reads between one and
     * nine bytes.  Smaller values take fewer bytes.  Negative numbers are not
     * supported. */
    public long readVLong() throws IOException {
        /* This is the original code of this method,
         * but a Hotspot bug (see LUCENE-2975) corrupts the for-loop if
         * readByte() is inlined. So the loop was unwinded!
        byte b = readByte();
        long i = b & 0x7F;
        for (int shift = 7; (b & 0x80) != 0; shift += 7) {
          b = readByte();
          i |= (b & 0x7FL) << shift;
        }
        return i;
        */
        byte b = readByte();
        long i = b & 0x7FL;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7FL) << 7;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7FL) << 14;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7FL) << 21;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7FL) << 28;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7FL) << 35;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7FL) << 42;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        i |= (b & 0x7FL) << 49;
        if ((b & 0x80) == 0)
            return i;
        b = readByte();
        assert (b & 0x80) == 0;
        return i | ((b & 0x7FL) << 56);
    }

    /** Reads a string.
     * @see DataOutput#writeString(String)
     */
    public String readString() throws IOException {
        if (preUTF8Strings)
            return readModifiedUTF8String();
        int length = readVInt();
        final byte[] bytes = new byte[length];
        readBytes(bytes, 0, length);
        return new String(bytes, 0, length, "UTF-8");
    }

    private String readModifiedUTF8String() throws IOException {
        int length = readVInt();
        final char[] chars = new char[length];
        readChars(chars, 0, length);
        return new String(chars, 0, length);
    }

    /** Reads Lucene's old "modified UTF-8" encoded
     *  characters into an array.
     * @param buffer the array to read characters into
     * @param start the offset in the array to start storing characters
     * @param length the number of characters to read
     * @see DataOutput#writeChars(String,int,int)
     * @deprecated -- please use readString or readBytes
     *                instead, and construct the string
     *                from those utf8 bytes
     */
    @Deprecated
    public void readChars(char[] buffer, int start, int length) throws IOException {
        final int end = start + length;
        for (int i = start; i < end; i++) {
            byte b = readByte();
            if ((b & 0x80) == 0)
                buffer[i] = (char) (b & 0x7F);
            else if ((b & 0xE0) != 0xE0) {
                buffer[i] = (char) (((b & 0x1F) << 6) | (readByte() & 0x3F));
            } else {
                buffer[i] = (char) (((b & 0x0F) << 12) | ((readByte() & 0x3F) << 6) | (readByte() & 0x3F));
            }
        }
    }

    /** Returns a clone of this stream.
     *
     * <p>Clones of a stream access the same data, and are positioned at the same
     * point as the stream they were cloned from.
     *
     * <p>Expert: Subclasses must ensure that clones may be positioned at
     * different points in the input from each other and from the stream they
     * were cloned from.
     */
    @Override
    public Object clone() {
        DataInput clone = null;
        try {
            clone = (DataInput) super.clone();
        } catch (CloneNotSupportedException e) {
        }

        return clone;
    }

    public Map<String, String> readStringStringMap() throws IOException {
        final Map<String, String> map = new HashMap<String, String>();
        final int count = readInt();
        for (int i = 0; i < count; i++) {
            final String key = readString();
            final String val = readString();
            map.put(key, val);
        }

        return map;
    }
}
